1. Field of the Invention
The present invention relates to an elastic wave device preferably for use in a resonator, a bandpass filter, or the like and a method for manufacturing the same. More particularly, the present invention relates to an elastic wave device having a structure including a supporting substrate, a piezoelectric layer, and a layer of another material disposed therebetween, and a method for manufacturing the same.
2. Description of the Related Art
Elastic wave devices have been widely used as resonators and bandpass filters, and in recent years, there has been a need for increasing the frequency thereof. Japanese Unexamined Patent Application Publication No. 2004-282232 described below discloses a surface acoustic wave device in which a hard dielectric layer, a piezoelectric film, and an IDT electrode are stacked in that order on a dielectric substrate. In such a surface acoustic wave device, by disposing the hard dielectric layer between the dielectric substrate and the piezoelectric film, an increase in the acoustic velocity of surface acoustic waves is achieved. It is described that thereby, the frequency of the surface acoustic wave device can be increased.
Japanese Unexamined Patent Application Publication No. 2004-282232 also discloses a structure in which a potential equalizing layer is provided between the hard dielectric layer and the piezoelectric film. The potential equalizing layer is composed of a metal or semiconductor. The potential equalizing layer is provided in order to equalize the potential at the interface between the piezoelectric film and the hard dielectric layer.
In the surface acoustic wave device described in Japanese Unexamined Patent Application Publication No. 2004-282232, an increase in acoustic velocity is achieved by forming the hard dielectric layer. However, there is considerable propagation loss, and surface acoustic waves cannot be effectively confined within the piezoelectric thin film. Consequently, the energy of the surface acoustic wave device leaks into the dielectric substrate, and therefore, it is not possible to enhance the Q factor, which is a problem.